Because Blue-Green is the medium between Blue (4.5-5)x10^-7 and Green (5.0-5.7)x10^-7, as the light in this example is 5x10^-7, so it falls between the two. Have you any though on the first question?
Homework Statement
If an electron in metallic cesium absorbs a photon of red light (6.6x10^-7) m in vacuum), all the energy is used up in escaping from the attractive forces in the metal. Suppose light with 5x10^-7 is used, what percentage of the photon's energy does the electron retain after...